A knowledge-based approach for fuzzy information retrieval is proposed, where interval queries and weighted-interval queries are allowed for document retrieval, In this paper, knowledge is represented by a concept matrix, where the elements in a concept matrix represent relevant values between concepts, The implicit relevant values between concepts are inferred by the transitive closure of the concept matrix based on fuzzy logic. The proposed method is more flexible than the ones presented in [6] and [11] due to the fact that it has the capability to deal with interval queries and weighted-interval queries.